Replies to Minipulse Plus

[Qiaozhi]

Frankly, non-motion makes more sense, and with additional LP it will most probably take care of the residual charge injection spikes and become more calm.

The problem with non-motion is drift, which requires the operator to constantly tweak the threshold control. A third variation would be to replace R29 with a 1M pot in series with a 100k resistor, so the SAT speed can be adjusted.

Remember the MPP was created as an alternative to the Surf-PI and Baracuda designs, and to be an easier project to assemble (with a greater chance of successfully ending up with a working detector), with a faster preamp for early sampling, and the minimum of options and adjustments. It was also intended as a good experimental platform for more knowledgeable Geotech members to try out new ideas, add extra features, or make various improvements. I expect the MPP design to basically stay as it is, but other variants may emerge in the future from the efforts of various members.

Later versions of the Build Document may include an Advanced Topics appendix, which could describe additions such as how to add an adjustable SAT, and switch between motion and non-motion modes. More advanced stuff, such as GB that would need additional components, would require a new PCB layout. In this case, we would need to create a new variant, maybe called MPP-GB (for example).

[ivconic]

Ok, here is schematic we can work on together Davor.
You may add your mod on it or i can do that with your help, whatever.

[Qiaozhi]

Ivica - For your info: I've just replaced the LT1054 with an ICL7660A, and there was no problem with the audio. So it looks like you have a different problem.

[Davor]

Ok, here is schematic we can work on together Davor.
You may add your mod on it or i can do that with your help, whatever.

I'll make the GB circuit on a protoboard and see what happens and what part values will be the best for it. The rest of the mods will come as I (finally) start building the device. I completed inventory of the parts on stock and I'll start making something. I should make some provisory coil just to have something to play with on a table.

[multieagle]

Battery question:

Would a battery pack such as this work: http://www.ebay.ca/itm/12V-Genuine-3...item2a2508189c

Or same battery, larger dimensions?

Thanks

[Qiaozhi]

Battery question:

Would a battery pack such as this work: http://www.ebay.ca/itm/12V-Genuine-3...item2a2508189c

Or same battery, larger dimensions?

Thanks

That looks a good choice.
The 3000mAh capacity will give a long detecting time with the MPP.

[ivconic]

Ivica - For your info: I've just replaced the LT1054 with an ICL7660A, and there was no problem with the audio. So it looks like you have a different problem.

Good to know that too, thanks!

[josewashere]

Hi Multieagle
I used the larger 6.8amp version of that battery in mine. The 3 amp version at about 30 hours of operation is big enough though. If like mine its got a switch on the side then you can hack into the side of the battery around the switch and remove it. Then you can extend the three wires of the switch and led to your own switch and led on your detector. Output lead of battery goes to mmp and input charge lead goes to charge socket on mmp

[ivconic]

Ok, i did two more better videos.
I must point you on few facts to keep on mind before watching them:
1) Coil is catastrophic! I made it on hurry just to test if detector functioning at all, windings are bulky and mess. 300uH
2) I did as Davor suggested; put LF353 instead TL062, can't say that i noticed significant changes.
3) R29 (1M) is now 2M2, SAT period is bit extended, just what i wanted to achieve. Lower values do decrease period.
4) Speaker is 100 ohms, audio is significantly better than with 8 ohms speaker.
5) There are short comments under the videos, no need for further explanations... hopefully!

Qiaozhi did a good job, there is noticeable rejection which is working by logic quite opposite than conventional discrimination.
Must say that this works exactly the same as at Delta Pulse, but considering higher pps now this is having much more sense... at least to me.
Ok, enough me talking, enjoy!

First video (No Rejection):

[ivconic]

Ooops! I can't post 2 videos in one reply!?

"...You have included a total of 2 videos in your message. The maximum number that you may include is 1...."

Ok, here is the second one (Rejection):

[joop]

Just wondering.... Should I be able to detect a small piece (1x1 cm) of ALU foil with the minipuse plus? It does not give a sound, even with the delay set below 10 microseconds. I believe I read somewhere that aluminium foil is a good indication for gold sensivity....

[ivconic]

Just wondering.... Should I be able to detect a small piece (1x1 cm) of ALU foil with the minipuse plus? It does not give a sound, even with the delay set below 10 microseconds. I believe I read somewhere that aluminium foil is a good indication for gold sensivity....

I know i missed something to do, now i know what; to test it on Al foil, damn!
I will do that next time.

[Qiaozhi]

Just wondering.... Should I be able to detect a small piece (1x1 cm) of ALU foil with the minipuse plus? It does not give a sound, even with the delay set below 10 microseconds. I believe I read somewhere that aluminium foil is a good indication for gold sensivity....

A 0.47 gram nugget (7.25 grains) can be emulated with a 9mm x 9mm aluminium square from the side wall of a Cola can. Your 10mm x 10mm square of aluminium foil is much thinner, so I doubt you'll be able to detect it.

[Davor]

George, could you please post a sort of specification on timings in form of spans; delay to first sample (min, max), first sample duration (min, max), delay to EF (min, max)
Thanks.

[joop]

A 0.47 gram nugget (7.25 grains) can be emulated with a 9mm x 9mm aluminium square from the side wall of a Cola can. Your 10mm x 10mm square of aluminium foil is much thinner, so I doubt you'll be able to detect it.

Thanks! I cut a 10x10 piece out of a alu can. I can detect it with a delay of 6-7 microseconds. My coil has an average diameter of 21 cm, so it might be a bit big for small stuff. I am pleased I can still detect the aluminium piece.

I think this is good test! The coil is 360 uH with a 280 Ohm resistor, which I optimised by watching the receiver opamp output. I will try and see if this test can also be used to optimise the coil resistor....

I also took a 15x15 piece of alu from the can, to see if I could reject it. With the 100k reject pot I can barely reject it at full scale, which is about 40 uS. Pulltabs are still very loud. So I am thinking about making the reject pot much larger, maybe 250k?